docstr: Emulate the case ray.shutdown is called
  and the core_worker instance is GC'ed.
docstr_tok: ["Emulate","the","case","ray.shutdown","is","called","and","the","core_worker","instance","is","GC'ed","."]
code: def reset_core_worker(self):
      """Emulate the case ray.shutdown is called
      and the core_worker instance is GC'ed.
      """
      self.core_worker = None
  
imports: import asyncio
  import pytest
  import numpy
  import sys
  import time
  import threading
  import gc
  from unittest.mock import patch, Mock
  import ray
  from ray._private.test_utils import wait_for_condition
  from ray.experimental.state.api import list_objects
  from ray._raylet import ObjectRefGenerator, ObjectRefStreamEndOfStreamError
  from ray.cloudpickle import dumps
  from ray.exceptions import WorkerCrashedError
label_desc: Use image node_id 2 for calling the MockedWorker obj's underlying member method code with example usage: obj.reset_core_worker() without return types